CA2002142A1 - Process for increasing the useful life of a photovoltaic cell - Google Patents
Process for increasing the useful life of a photovoltaic cellInfo
- Publication number
- CA2002142A1 CA2002142A1 CA 2002142 CA2002142A CA2002142A1 CA 2002142 A1 CA2002142 A1 CA 2002142A1 CA 2002142 CA2002142 CA 2002142 CA 2002142 A CA2002142 A CA 2002142A CA 2002142 A1 CA2002142 A1 CA 2002142A1
- Authority
- CA
- Canada
- Prior art keywords
- copper indium
- layer
- metallic
- complex
- electrode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims abstract description 52
- 230000001965 increasing effect Effects 0.000 title abstract description 10
- HVMJUDPAXRRVQO-UHFFFAOYSA-N copper indium Chemical compound [Cu].[In] HVMJUDPAXRRVQO-UHFFFAOYSA-N 0.000 claims abstract description 55
- 239000011800 void material Substances 0.000 claims abstract description 16
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 15
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 15
- 150000004678 hydrides Chemical class 0.000 claims description 15
- 229910052719 titanium Inorganic materials 0.000 claims description 15
- 239000010936 titanium Substances 0.000 claims description 15
- 229910052802 copper Inorganic materials 0.000 claims description 14
- 239000010949 copper Substances 0.000 claims description 14
- 229910052738 indium Inorganic materials 0.000 claims description 14
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 14
- 239000000243 solution Substances 0.000 claims description 13
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 10
- 229910052750 molybdenum Inorganic materials 0.000 claims description 10
- 239000011733 molybdenum Substances 0.000 claims description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 8
- 239000002184 metal Substances 0.000 claims description 8
- 239000002253 acid Substances 0.000 claims description 7
- -1 hydrogen ions Chemical class 0.000 claims description 7
- 229910052739 hydrogen Inorganic materials 0.000 claims description 5
- 239000001257 hydrogen Substances 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- 239000007864 aqueous solution Substances 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 239000011651 chromium Substances 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 claims description 3
- SPVXKVOXSXTJOY-UHFFFAOYSA-N selane Chemical compound [SeH2] SPVXKVOXSXTJOY-UHFFFAOYSA-N 0.000 claims description 2
- 229910000058 selane Inorganic materials 0.000 claims description 2
- 235000016768 molybdenum Nutrition 0.000 claims 6
- 239000002659 electrodeposit Substances 0.000 claims 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 claims 1
- 238000004070 electrodeposition Methods 0.000 abstract description 10
- 239000004065 semiconductor Substances 0.000 abstract description 6
- 230000015556 catabolic process Effects 0.000 abstract description 5
- 238000006731 degradation reaction Methods 0.000 abstract description 5
- 230000005855 radiation Effects 0.000 abstract description 2
- 150000004699 copper complex Chemical class 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 28
- 238000007747 plating Methods 0.000 description 14
- 239000010409 thin film Substances 0.000 description 7
- DOBRDRYODQBAMW-UHFFFAOYSA-N copper(i) cyanide Chemical compound [Cu+].N#[C-] DOBRDRYODQBAMW-UHFFFAOYSA-N 0.000 description 5
- 150000002471 indium Chemical class 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 238000000151 deposition Methods 0.000 description 4
- SIXIBASSFIFHDK-UHFFFAOYSA-N indium(3+);trisulfide Chemical compound [S-2].[S-2].[S-2].[In+3].[In+3] SIXIBASSFIFHDK-UHFFFAOYSA-N 0.000 description 4
- PSCMQHVBLHHWTO-UHFFFAOYSA-K indium(iii) chloride Chemical compound Cl[In](Cl)Cl PSCMQHVBLHHWTO-UHFFFAOYSA-K 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 229910052980 cadmium sulfide Inorganic materials 0.000 description 3
- CJOBVZJTOIVNNF-UHFFFAOYSA-N cadmium sulfide Chemical compound [Cd]=S CJOBVZJTOIVNNF-UHFFFAOYSA-N 0.000 description 3
- 150000001879 copper Chemical class 0.000 description 3
- BWFPGXWASODCHM-UHFFFAOYSA-N copper monosulfide Chemical compound [Cu]=S BWFPGXWASODCHM-UHFFFAOYSA-N 0.000 description 3
- ORTQZVOHEJQUHG-UHFFFAOYSA-L copper(II) chloride Chemical compound Cl[Cu]Cl ORTQZVOHEJQUHG-UHFFFAOYSA-L 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 206010073306 Exposure to radiation Diseases 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 239000005864 Sulphur Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- LCUOIYYHNRBAFS-UHFFFAOYSA-N copper;sulfanylideneindium Chemical compound [Cu].[In]=S LCUOIYYHNRBAFS-UHFFFAOYSA-N 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000011833 salt mixture Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 description 1
- BWGNESOTFCXPMA-UHFFFAOYSA-N Dihydrogen disulfide Chemical compound SS BWGNESOTFCXPMA-UHFFFAOYSA-N 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000006096 absorbing agent Substances 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 230000009918 complex formation Effects 0.000 description 1
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 1
- OMZSGWSJDCOLKM-UHFFFAOYSA-N copper(II) sulfide Chemical compound [S-2].[Cu+2] OMZSGWSJDCOLKM-UHFFFAOYSA-N 0.000 description 1
- UIPVMGDJUWUZEI-UHFFFAOYSA-N copper;selanylideneindium Chemical class [Cu].[In]=[Se] UIPVMGDJUWUZEI-UHFFFAOYSA-N 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000011221 initial treatment Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 238000011282 treatment Methods 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 238000002424 x-ray crystallography Methods 0.000 description 1
Landscapes
- Photovoltaic Devices (AREA)
Abstract
PROCESS FOR INCREASING THE USEFUL
LIFE OF A PHOTOVOLTAIC CELL
ABSTRACT
A process for forming a chalcogenated copper complex layer on a metallic electrode for use in a photovoltaic cell. The layer is formed by a three-step process involving electrodeposition of a copper indium complex. The process produces a void free copper indium semiconductor layer which resists degradation when exposed to radiation and thereby increases the useful life of the photovoltaic cell.
LIFE OF A PHOTOVOLTAIC CELL
ABSTRACT
A process for forming a chalcogenated copper complex layer on a metallic electrode for use in a photovoltaic cell. The layer is formed by a three-step process involving electrodeposition of a copper indium complex. The process produces a void free copper indium semiconductor layer which resists degradation when exposed to radiation and thereby increases the useful life of the photovoltaic cell.
Description
2~021~2 Docket No. 70-241 PROCESS FOR INCREASING THE USEFUL
LIFE OF A PHOTOVOLTAIC CELL
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates generally to increas-ing the useful life of heterojunction photovoltaic cells or devices which utilize chalcogenated copper indium complexes as one of the cell layers. More particularly, the present invention relates to an electrodeposition process in which a void free chalcogenated copper indium complex layer is produced to thereby extend the cell useful life.
2. Description of Related Art.
1 Photovoltaic devices utilizing thin films of cadmium sulphide and copper sulphide (Cds/Cu2S) were developed in the 1950s and early 1960s. Extensive research and development in connection with these cells has resulted in the development of devices having conversion efficiencies of up to ten percent (10%).
Such high conversion efficiencies make such cells competitive with the conventional thin film silicon-based solar cells. Accordingly, there has been a great deal of interest in developing Cds/Cu2S cells which are suitable for commercial applications.
A major problem which has been experienced with Cds/Cu2S devices is degradation of the semiconductor film integrity over extended periods of time resulting in decreased cell efficiency. Accordingly, there has been a great deal of investigation conducted into the mechanisms which cause the gradual degradation of the Cds/Cu2S cell efficiency. Although numerous theories have been proposed as to the possible reasons for cell deqradation, no entirely acceptable solution has yet been found.
: .., :.; " :, ' "~. ~
4~
Docket No. 70-241 , Photovoltaic devices have also been developed in which chalcogenated copper indium complexes have been used in place of copper sulfide. The chalcogenated copper indium complexes which have been of particular interest include copper indium disulfide (CuInS2), copper indium diselinide (CuInSe2) and copper indium sulfide (CuIn5S8). These new type of cells, based on thin films of cadmium sulphide and chalcogenated copper indium complexes, are of interest because they provide higher efficiencies and a higher speed of production than was possible with the prior solar cells utilizing -~
copper sulphide. However, a common problem which these cells have experienced is the gradual degradation of ~-~
cell efficiency upon exposure to radiation.
It is believed that voids in the thin film struc-tures are the main reason for the gradual decay in performance of these solar cells. Accordingly, a major obstacle which must be overcome in order to provide solar cells having increased useful life is the elimina~
tion of voids and other irregularities in the thin film ;
structure. A number of different thin film formation techniques have been utilized in order to provide structures that are void free. Such processes have included sputter deposition, chemical vapor deposition and electrodeposition. Although the films produced by these processes are acceptable for use in photovoltaic cells, they have not been entirely void free. Accord-ingly, there still is a continuing need for an improved process wherein the deposited film is free of voids or imperfections. Such a process for depositing void free thin films is necessary in order to increase the service life of photovoltaic cells and thereby enhance their commercial value.
: ~ .
. :
~2142 Docket No. 70-241 SUMMARY OF THE INVENTION
In accordance with the present invention, a process is provided for forming a photovoltaic cell having increased service life due to the deposition of a void free semiconductor layer.
The present invention is based on the discovery that a thin, void free layer of chalcogenated copper indium complex may be formed on a metallic electrode layer according to the following three step process.
First, the surface of the metallic electrode layer is initially treated with hydrogen ions to form metallic hydrides thereon. A copper indium complex is then electrodeposited onto the metallic hydride surface of the electrode followed by chalcogenation to form the chalcogenated copper indium complex. This process produces a chalcogenated copper indium complex layer on the metallic electrode which is void free and therefore resistant to degradation upon exposure to radiation.
As a feature of the present invention, the electro~
deposition of the copper indium complex involves applying an alternating electric current of preset frequency to an aqueous solution of a copper indium complex. The relative amounts of copper and indium in the complex solution along with the frequency and potential of the alternating electric current are controlled so that the deposited copper indium complex has a copper to indium ratio of 1:1. Upon chalcogena-tion of the deposited copper indium complex, a thin layer is formed which is especially well-suited to provide an extended service photovoltaic cell.
The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better under-stood by reference to the following detailed description when considered in conjunction with the accompanying drawing.
'' ''. ~` "~ '' `' 2~2~42 Docket No. 70-241 BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic sectional view of an exemplary photovoltaic cell made in accordance with the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An exemplary photovoltaic device in accordance with the present invention is shown generally at lo in the drawing. The arrows 20 indicate the direction from which radiation is directed onto the cell during operation.
The photovoltaic device or cell 10 includes a transparent substrate 11 which is conventionally made from glass or other suitable material. A metallic electrode 12 is attached to the substrate 11 as is conventionally known. The electrode 12 may be made from any of the electrode materials conventionally used in photovoltaic cells. As is also known, a semiconductor layer 13 is provided which is preferably made from cadmium sulphide or similar materials. This semicon-ductor layer 13 is typically from about 0.2 to 40 micrometers thicX. The elements 11, 12 and 13 as shown in the Figure are all conventional and do not form part of applicant's invention. Rather, applicant's invention is directed to the deposition of a layer 14 of chalco-genated copper indium complex onto a metallic electrode layer 15. The chalcogenated copper indium complex layer 14 is also known as an absorber layer. The method by which the other layers 11-13 are attached to or formed on the combined chalcogenated copper indium complex layer 14 and alectrode layer 15 are also well known in the art.
The following description will be limited to the process for forming the chalcogenated copper indium complex layer 14 on the electrode layer 15 in accordance `~ '. ~"'.
2~02~A2 Docket No. 70-241 with the present invention. The other elements utilized in the photovoltaic device will not be further described as they are all well known in the art and applicant's invention may be utilized with any of the related 5cadmium sulphur semiconductors and photovoltaic layer configurations.
The first step in applicant's process involves treating a metallic electrode layer with hydrogen ions prior to electrodeposition of the copper indium complex.
10This initial treatment forms metallic hydrides on the surface of the metallic electrode. Although any material conventionally used as a metallic electrode in photovoltaic devices may be used, it is preferred that titanium, molybdenum, chromium, nickel and their alloys 15be used. Particularly preferred is pure titanium or pure molybdenum.
The formation of metallic hydrides on the surface of the metal is preferably accomplished by treatment with sulfuric acid or alternatively, hydrochloric acid.
20The methods for treating metals with acids to form a surface layer of hydrides is known in the art and will not be described in detail. The important consideration is that the metallic surface be treated with the acid under conventional conditions to create a surface layer 25of metallic hydride without destroying or otherwise degrading the metal.
The next step in the process involves electrodepo-siting a copper indium complex onto the metallic hydride i electrode surface. The electrodeposition is carried out 30according to a known procedure utilizing an alternating current electrodeposition process wherein the metallic electrode is emersed in an electrolysis bath including an aqueous mixture of copper and indium salts. This procedure is also known as a metalfusion process which 35is described in detail in U.S. Patent No. 4,566,992, the contents of which are hereby incorporated by reference.
.'' ~,,:' "
' '' ' ' '.
~` 2~2~42 .
Docket No. 70-241 The electrolysis bath or plating solution should be an alkaline aqueous solution having a pH of at least 7-9. The pH of the plating bath may be increased to higher levels provided that the pH is not increased to the point at which copper precipitates from the solu-tion. The plating bath should be maintained at a temperature of between 100 - 150 C, with a temperature of approximately 135-C being preferred.
The ma;or inqredients of the plating bath are dissolved salts of copper and indium. Suitable copper salts include copper cyanide, copper sulphate or copper chloride. Suitable salts of indium include indium chloride and indium sulphide. It is preferred that the indium salt added to the plating bath be a mixture of indium chloride and indium sulphide. The relative amounts of indium chloride and indium sulphide should be approximately equal. Copper cyanide may be used alone as the copper salt in the plating bath. However, when copper sulphide or copper chloride is used as the source of copper salt, then it is preferred that both of these salts be added to the plating bath in equal amounts.
The total concentration of copper and indium salts present in the plating bath is preferably maintained between 2 percent by weight and 10 percent by weight.
The relative amounts of copper and indium in the bath should be about 60 to 70 weight percent copper and 30 to weight percent indium. Other additives conven~
tionally utilized in plating baths may be included if desired, provided that they do not adversely affect the electrodeposited copper indium complex.
In conducting the actual electrodeposition step, it is important that the ratio of copper to indium present in the deposited complex be 1:1. It was discovered that ratios of copper to indium which were not 1:1 resulted in the formation of voids and other irregularities in the deposited layer. In order to achieve the desired .',. ': '.,-~=
200~42 Docket No. 70-241 - -,:, . .: ~
complex formation, it is important that the electrical potential applied to the electrolysis bath be within certain voltage limits and frequency parameters. The preferred voltage range is from 0.1 volt to 1.0 volt with 0.5 volt being preferred. The potential is applied as an alternating current which has a frequency of between 109,000 Hertz and 122,000 Hertz. The preferred frequency is about 114,000 Hertz. It is possible to obtain suitable void free layers utilizing direct current electrodeposition. However, the direct current electrodeposition requires an additional etching step and therefore is not preferred.
The electrodeposition process is carried out within the above-described parameters for a sufficient time to deposit a layer which is between about 10 angstroms to 5 microns thick. This copper indium complex layer, as mentioned above, must have a ratio of copper to indium of 1:1 and as a result, will be void free. Verification that the proper conditions are being utilized is accomplished by X-ray crystallography, scanning electron microscopy or any other suitable technique for detecting voids in the structure of the complex layer.
The electrodeposited copper indium complex is then converted into the desired chalcogenated form in accordance with conventional procedures. Chalcogena-tion, as used herein, is the procedure for converting a copper indium complex into copper indium sulphur compounds or copper indium selenide compounds. The preferred chalcogenated copper indium complexes are CuInS2, CuInSe2 and CuIn5S8. The procedures for chalcogenating copper indium complexes are convention~
ally known. They typically involve exposing the copper indium complex to an atmosphere of hydrogen sulphide or hydrogen selenide depending upon the particular chalco-genated complex desired. The methods for chalcogenatinqcopper indium complexes is well known and does not form ,- .:~`: ~ "
,, 2~21AZ
Docket No. 70-241 part of the invention other than it is required that the electrodeposited copper indium complex be converted to the desired chalcogenated complex in order for it to be useful in a photovoltaic cell. Accordingly, the details of the procedures used for chalcogenating copper indium complexes will not be further described.
Examples of practice are as follows.
Example 1 A pure titanium metal electrode having the dimen-sions of one inch (2.54 centimeters) by one inch (2.54 centimeters) by 0.020 inch (0.05 centimeters) was immersed in a ten percent (10%) sulphur acid solution for approximately two minutes. The electrode was then removed from the acid solution, flushed with distilled water and dried. The time of immersion may vary depending upon temperature and acid concentrations.
Accordingly, under different conditions, the electrode should be immersed until the surface of the titanium turns from dark gray to black.
The plating bath was a Rochelle cyanide solution of copper and indium, with the amounts of copper and indium being sixty percent (60%) by weight and forty percent (40%) by weight, respectively. The solution was prepared by dissolving 8 grams of copper cyanide and 12 grams of an indium/salt mixture containing equal amounts of indium chloride and indium sulphide in 1 liter of water. This provides a 2 weight percent aqueous solution of the salts. The pH of the plating bath was . .
LIFE OF A PHOTOVOLTAIC CELL
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates generally to increas-ing the useful life of heterojunction photovoltaic cells or devices which utilize chalcogenated copper indium complexes as one of the cell layers. More particularly, the present invention relates to an electrodeposition process in which a void free chalcogenated copper indium complex layer is produced to thereby extend the cell useful life.
2. Description of Related Art.
1 Photovoltaic devices utilizing thin films of cadmium sulphide and copper sulphide (Cds/Cu2S) were developed in the 1950s and early 1960s. Extensive research and development in connection with these cells has resulted in the development of devices having conversion efficiencies of up to ten percent (10%).
Such high conversion efficiencies make such cells competitive with the conventional thin film silicon-based solar cells. Accordingly, there has been a great deal of interest in developing Cds/Cu2S cells which are suitable for commercial applications.
A major problem which has been experienced with Cds/Cu2S devices is degradation of the semiconductor film integrity over extended periods of time resulting in decreased cell efficiency. Accordingly, there has been a great deal of investigation conducted into the mechanisms which cause the gradual degradation of the Cds/Cu2S cell efficiency. Although numerous theories have been proposed as to the possible reasons for cell deqradation, no entirely acceptable solution has yet been found.
: .., :.; " :, ' "~. ~
4~
Docket No. 70-241 , Photovoltaic devices have also been developed in which chalcogenated copper indium complexes have been used in place of copper sulfide. The chalcogenated copper indium complexes which have been of particular interest include copper indium disulfide (CuInS2), copper indium diselinide (CuInSe2) and copper indium sulfide (CuIn5S8). These new type of cells, based on thin films of cadmium sulphide and chalcogenated copper indium complexes, are of interest because they provide higher efficiencies and a higher speed of production than was possible with the prior solar cells utilizing -~
copper sulphide. However, a common problem which these cells have experienced is the gradual degradation of ~-~
cell efficiency upon exposure to radiation.
It is believed that voids in the thin film struc-tures are the main reason for the gradual decay in performance of these solar cells. Accordingly, a major obstacle which must be overcome in order to provide solar cells having increased useful life is the elimina~
tion of voids and other irregularities in the thin film ;
structure. A number of different thin film formation techniques have been utilized in order to provide structures that are void free. Such processes have included sputter deposition, chemical vapor deposition and electrodeposition. Although the films produced by these processes are acceptable for use in photovoltaic cells, they have not been entirely void free. Accord-ingly, there still is a continuing need for an improved process wherein the deposited film is free of voids or imperfections. Such a process for depositing void free thin films is necessary in order to increase the service life of photovoltaic cells and thereby enhance their commercial value.
: ~ .
. :
~2142 Docket No. 70-241 SUMMARY OF THE INVENTION
In accordance with the present invention, a process is provided for forming a photovoltaic cell having increased service life due to the deposition of a void free semiconductor layer.
The present invention is based on the discovery that a thin, void free layer of chalcogenated copper indium complex may be formed on a metallic electrode layer according to the following three step process.
First, the surface of the metallic electrode layer is initially treated with hydrogen ions to form metallic hydrides thereon. A copper indium complex is then electrodeposited onto the metallic hydride surface of the electrode followed by chalcogenation to form the chalcogenated copper indium complex. This process produces a chalcogenated copper indium complex layer on the metallic electrode which is void free and therefore resistant to degradation upon exposure to radiation.
As a feature of the present invention, the electro~
deposition of the copper indium complex involves applying an alternating electric current of preset frequency to an aqueous solution of a copper indium complex. The relative amounts of copper and indium in the complex solution along with the frequency and potential of the alternating electric current are controlled so that the deposited copper indium complex has a copper to indium ratio of 1:1. Upon chalcogena-tion of the deposited copper indium complex, a thin layer is formed which is especially well-suited to provide an extended service photovoltaic cell.
The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better under-stood by reference to the following detailed description when considered in conjunction with the accompanying drawing.
'' ''. ~` "~ '' `' 2~2~42 Docket No. 70-241 BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic sectional view of an exemplary photovoltaic cell made in accordance with the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An exemplary photovoltaic device in accordance with the present invention is shown generally at lo in the drawing. The arrows 20 indicate the direction from which radiation is directed onto the cell during operation.
The photovoltaic device or cell 10 includes a transparent substrate 11 which is conventionally made from glass or other suitable material. A metallic electrode 12 is attached to the substrate 11 as is conventionally known. The electrode 12 may be made from any of the electrode materials conventionally used in photovoltaic cells. As is also known, a semiconductor layer 13 is provided which is preferably made from cadmium sulphide or similar materials. This semicon-ductor layer 13 is typically from about 0.2 to 40 micrometers thicX. The elements 11, 12 and 13 as shown in the Figure are all conventional and do not form part of applicant's invention. Rather, applicant's invention is directed to the deposition of a layer 14 of chalco-genated copper indium complex onto a metallic electrode layer 15. The chalcogenated copper indium complex layer 14 is also known as an absorber layer. The method by which the other layers 11-13 are attached to or formed on the combined chalcogenated copper indium complex layer 14 and alectrode layer 15 are also well known in the art.
The following description will be limited to the process for forming the chalcogenated copper indium complex layer 14 on the electrode layer 15 in accordance `~ '. ~"'.
2~02~A2 Docket No. 70-241 with the present invention. The other elements utilized in the photovoltaic device will not be further described as they are all well known in the art and applicant's invention may be utilized with any of the related 5cadmium sulphur semiconductors and photovoltaic layer configurations.
The first step in applicant's process involves treating a metallic electrode layer with hydrogen ions prior to electrodeposition of the copper indium complex.
10This initial treatment forms metallic hydrides on the surface of the metallic electrode. Although any material conventionally used as a metallic electrode in photovoltaic devices may be used, it is preferred that titanium, molybdenum, chromium, nickel and their alloys 15be used. Particularly preferred is pure titanium or pure molybdenum.
The formation of metallic hydrides on the surface of the metal is preferably accomplished by treatment with sulfuric acid or alternatively, hydrochloric acid.
20The methods for treating metals with acids to form a surface layer of hydrides is known in the art and will not be described in detail. The important consideration is that the metallic surface be treated with the acid under conventional conditions to create a surface layer 25of metallic hydride without destroying or otherwise degrading the metal.
The next step in the process involves electrodepo-siting a copper indium complex onto the metallic hydride i electrode surface. The electrodeposition is carried out 30according to a known procedure utilizing an alternating current electrodeposition process wherein the metallic electrode is emersed in an electrolysis bath including an aqueous mixture of copper and indium salts. This procedure is also known as a metalfusion process which 35is described in detail in U.S. Patent No. 4,566,992, the contents of which are hereby incorporated by reference.
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Docket No. 70-241 The electrolysis bath or plating solution should be an alkaline aqueous solution having a pH of at least 7-9. The pH of the plating bath may be increased to higher levels provided that the pH is not increased to the point at which copper precipitates from the solu-tion. The plating bath should be maintained at a temperature of between 100 - 150 C, with a temperature of approximately 135-C being preferred.
The ma;or inqredients of the plating bath are dissolved salts of copper and indium. Suitable copper salts include copper cyanide, copper sulphate or copper chloride. Suitable salts of indium include indium chloride and indium sulphide. It is preferred that the indium salt added to the plating bath be a mixture of indium chloride and indium sulphide. The relative amounts of indium chloride and indium sulphide should be approximately equal. Copper cyanide may be used alone as the copper salt in the plating bath. However, when copper sulphide or copper chloride is used as the source of copper salt, then it is preferred that both of these salts be added to the plating bath in equal amounts.
The total concentration of copper and indium salts present in the plating bath is preferably maintained between 2 percent by weight and 10 percent by weight.
The relative amounts of copper and indium in the bath should be about 60 to 70 weight percent copper and 30 to weight percent indium. Other additives conven~
tionally utilized in plating baths may be included if desired, provided that they do not adversely affect the electrodeposited copper indium complex.
In conducting the actual electrodeposition step, it is important that the ratio of copper to indium present in the deposited complex be 1:1. It was discovered that ratios of copper to indium which were not 1:1 resulted in the formation of voids and other irregularities in the deposited layer. In order to achieve the desired .',. ': '.,-~=
200~42 Docket No. 70-241 - -,:, . .: ~
complex formation, it is important that the electrical potential applied to the electrolysis bath be within certain voltage limits and frequency parameters. The preferred voltage range is from 0.1 volt to 1.0 volt with 0.5 volt being preferred. The potential is applied as an alternating current which has a frequency of between 109,000 Hertz and 122,000 Hertz. The preferred frequency is about 114,000 Hertz. It is possible to obtain suitable void free layers utilizing direct current electrodeposition. However, the direct current electrodeposition requires an additional etching step and therefore is not preferred.
The electrodeposition process is carried out within the above-described parameters for a sufficient time to deposit a layer which is between about 10 angstroms to 5 microns thick. This copper indium complex layer, as mentioned above, must have a ratio of copper to indium of 1:1 and as a result, will be void free. Verification that the proper conditions are being utilized is accomplished by X-ray crystallography, scanning electron microscopy or any other suitable technique for detecting voids in the structure of the complex layer.
The electrodeposited copper indium complex is then converted into the desired chalcogenated form in accordance with conventional procedures. Chalcogena-tion, as used herein, is the procedure for converting a copper indium complex into copper indium sulphur compounds or copper indium selenide compounds. The preferred chalcogenated copper indium complexes are CuInS2, CuInSe2 and CuIn5S8. The procedures for chalcogenating copper indium complexes are convention~
ally known. They typically involve exposing the copper indium complex to an atmosphere of hydrogen sulphide or hydrogen selenide depending upon the particular chalco-genated complex desired. The methods for chalcogenatinqcopper indium complexes is well known and does not form ,- .:~`: ~ "
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Docket No. 70-241 part of the invention other than it is required that the electrodeposited copper indium complex be converted to the desired chalcogenated complex in order for it to be useful in a photovoltaic cell. Accordingly, the details of the procedures used for chalcogenating copper indium complexes will not be further described.
Examples of practice are as follows.
Example 1 A pure titanium metal electrode having the dimen-sions of one inch (2.54 centimeters) by one inch (2.54 centimeters) by 0.020 inch (0.05 centimeters) was immersed in a ten percent (10%) sulphur acid solution for approximately two minutes. The electrode was then removed from the acid solution, flushed with distilled water and dried. The time of immersion may vary depending upon temperature and acid concentrations.
Accordingly, under different conditions, the electrode should be immersed until the surface of the titanium turns from dark gray to black.
The plating bath was a Rochelle cyanide solution of copper and indium, with the amounts of copper and indium being sixty percent (60%) by weight and forty percent (40%) by weight, respectively. The solution was prepared by dissolving 8 grams of copper cyanide and 12 grams of an indium/salt mixture containing equal amounts of indium chloride and indium sulphide in 1 liter of water. This provides a 2 weight percent aqueous solution of the salts. The pH of the plating bath was . .
3.6. The dried titanium electrode was immersed in the ~
.;: . . . ~
plating bath solution for approximately two minutes at a `
platin~ bath temperature of 140C. During ``~`, electroplating, an electric impulse was applied to the bath in the form a square wave having a frequency of approximately 114, ono Hertz and a potential of 0.5 EV.
The titanium electrode was then removed from the plating , ., . ~ .: :~ ,.
', , , ' .
2~as2 ";
Docket No. 70-241 bath with the electrodeposited coating of copper indium complex covering the entire surface.
The coating of copper indium complex on the titanium electrode was then chalcogenated by annealing at a temperature of 500C in the presence of hydrogen selenide (H2Se). A conventional chalcogenating appa- ~-ratus was utilized with the coated electrode being treated for approximately 20 minutes. The resulting electrode was coated with a void free layer of CuInSe2. - -'~' . '- "
Example 2 -~
The process according to Example 1 is carried out, except that molybdenum is substituted in place of titanium for the electrode metal. The process will produce a void free layer of CuInSe2 on the molybdenum electrode, which will provide increased photovoltaic cell life.
' .:-':~' ~,~
Example 3 The process is carried out in accordance with Example 1 except that the copper indium complex present on the titanium is treated with hydrogen sulphide during the chalcogenation step to thereby form CuInS2.
Example 4 The process set forth in Example 1 is followed except that 8 grams of copper chloride is substituted -~
for the copper cyanide. The pH of the bath is 5.2. The ~
~ coating which results on the electrode after chalcogena- ; ;
tion is void free.
Exam~le 5 The process is carried out according to Example 1 except that the amounts of copper cyanide and indium salt mixture are increased to 20 grams and 60 grams, respectively. The pH of the plating bath is 3.6. The 2~1~2~42 Docket No. 70-241 coating which results on the electrode after chalcogena-tion is void free.
. . .
Having thus described exemplary embodiments of the present invention, it should be noted by those skilled `
in the art that the within disclosures are exemplary ~`
only and that the various other alternatives, adapta-tions and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.
~''.'.'`'- `.'.'''" `'`' , ~" ~
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;
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plating bath solution for approximately two minutes at a `
platin~ bath temperature of 140C. During ``~`, electroplating, an electric impulse was applied to the bath in the form a square wave having a frequency of approximately 114, ono Hertz and a potential of 0.5 EV.
The titanium electrode was then removed from the plating , ., . ~ .: :~ ,.
', , , ' .
2~as2 ";
Docket No. 70-241 bath with the electrodeposited coating of copper indium complex covering the entire surface.
The coating of copper indium complex on the titanium electrode was then chalcogenated by annealing at a temperature of 500C in the presence of hydrogen selenide (H2Se). A conventional chalcogenating appa- ~-ratus was utilized with the coated electrode being treated for approximately 20 minutes. The resulting electrode was coated with a void free layer of CuInSe2. - -'~' . '- "
Example 2 -~
The process according to Example 1 is carried out, except that molybdenum is substituted in place of titanium for the electrode metal. The process will produce a void free layer of CuInSe2 on the molybdenum electrode, which will provide increased photovoltaic cell life.
' .:-':~' ~,~
Example 3 The process is carried out in accordance with Example 1 except that the copper indium complex present on the titanium is treated with hydrogen sulphide during the chalcogenation step to thereby form CuInS2.
Example 4 The process set forth in Example 1 is followed except that 8 grams of copper chloride is substituted -~
for the copper cyanide. The pH of the bath is 5.2. The ~
~ coating which results on the electrode after chalcogena- ; ;
tion is void free.
Exam~le 5 The process is carried out according to Example 1 except that the amounts of copper cyanide and indium salt mixture are increased to 20 grams and 60 grams, respectively. The pH of the plating bath is 3.6. The 2~1~2~42 Docket No. 70-241 coating which results on the electrode after chalcogena-tion is void free.
. . .
Having thus described exemplary embodiments of the present invention, it should be noted by those skilled `
in the art that the within disclosures are exemplary ~`
only and that the various other alternatives, adapta-tions and modifications may be made within the scope of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.
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Claims (21)
1. A process for forming a chalcogenated copper indium complex layer on a metallic electrode layer for use in a photovoltaic cell, said process comprising the steps of:
treating the surface of a metallic electrode layer with sufficient hydrogen ions to form a metallic hydride electrode surface having metallic hydrides thereon;
electrodepositing a layer of copper indium complex onto said metallic hydride electrode surface;
and chalcogenizing said layer of copper indium complex electrodeposited on said electrode surface to form a void free chalcogenated copper indium complex layer on said metallic electrode.
treating the surface of a metallic electrode layer with sufficient hydrogen ions to form a metallic hydride electrode surface having metallic hydrides thereon;
electrodepositing a layer of copper indium complex onto said metallic hydride electrode surface;
and chalcogenizing said layer of copper indium complex electrodeposited on said electrode surface to form a void free chalcogenated copper indium complex layer on said metallic electrode.
2. A process according to claim 1 wherein said metallic electrode comprises a metal selected from the group consisting of titanium, molybdenum, chromium and nickel.
3. A process according to claim 2 wherein said metallic electrode consists essentially of titanium or molybdenum.
4. A process according to claim 1 wherein the step of electrodepositing said copper indium complex onto said metallic hydride electrode surface comprises the steps of:
contacting said metallic hydride electrode surface with a copper indium complex solution;
applying a sufficient alternating electric potential to said electrode surface for a sufficient time and at a sufficient frequency to electrodeposit said copper indium complex onto said electrode surface.
contacting said metallic hydride electrode surface with a copper indium complex solution;
applying a sufficient alternating electric potential to said electrode surface for a sufficient time and at a sufficient frequency to electrodeposit said copper indium complex onto said electrode surface.
5. A process according to claim 4 wherein said copper indium complex solution is an aqueous solution comprising a copper indium cyanide complex.
6. A process according to claim 5 wherein the relative amounts of copper and indium in said copper indium complex are about to 60 to 70 weight percent copper and 30 to 40 weight percent indium.
7. A process according to claim 4 wherein the voltage of the applied electric potential is between about 0.1 and 1.0 volt.
8. A process according to claim 4 wherein the frequency of said alternating electric potential is between about 109,000 Hertz to 122,000 Hertz.
9. A process according to claim 7 wherein the electric potential is about 0.5 volt and the frequency of said alternating electric potential is about 114,000 Hertz.
10. A process according to claim 1 wherein treating the surface of said metallic electrode layer with hydrogen ions comprises the step of contacting said surface with an acid solution.
11. A process according to claim 10 wherein said acid solution is sulfuric acid or hydrochloric acid.
12. A process according to claim 1 wherein the step of chalcogenizing said deposited copper indium complex comprises the step of treating said complex with hydrogen sulfide or hydrogen selenide at a temperature which is sufficient to chalcogenate said copper indium complex.
13. A process according to claim 12 wherein said chalcogenated copper indium complex is CuInS2, CuInSe2 or CuIn5S8.
14. An article of manufacture comprises a layer of copper indium complex deposited on the surface of a metallic electrode layer, said article adopted for use in a photovoltaic cell, wherein said article is made by the process according to claim 1.
15. An article of manufacture according to claim 14 wherein said metallic electrode comprises a metal selected from the group consisting of titanium, molyb-denum, chromium and nickel.
16. An article of manufacture according to claim 15 wherein said metallic electrode consists essentially of titanium or molybdenum.
17. An article of manufacture according to claim 14 wherein said chalcogenated copper indium complex is CuInS2, CuInSe2 or CuIn5S8.
18. In a photovoltaic device including a layer of copper indium complex deposited on the surface of a metallic electrode, wherein the improvement comprises forming said layer of copper indium complex by the steps of:
treating the surface of a metallic electrode layer with sufficient hydrogen ions to form a metallic hydride electrode surface having metallic hydrides thereon;
electrodepositing a layer of copper indium complex onto said metallic hydride electrode surface;
and chalcogenizing said layer of copper indium complex electrodeposited on said electrode surface to form a void free chalcogenated copper indium complex layer on said metallic electrode.
treating the surface of a metallic electrode layer with sufficient hydrogen ions to form a metallic hydride electrode surface having metallic hydrides thereon;
electrodepositing a layer of copper indium complex onto said metallic hydride electrode surface;
and chalcogenizing said layer of copper indium complex electrodeposited on said electrode surface to form a void free chalcogenated copper indium complex layer on said metallic electrode.
19. The improvement of claim 18 wherein said metallic electrode comprises a metal selected from the group consisting of titanium, molybdenum, chromium and nickel.
20. The improvement of claim 19 wherein said metallic electrode consists essentially of titanium or molybdenum.
21. The improvement of claim 18 wherein said chalcogenated copper indium complex is CuInS2, CuInSe2 or CuIn5S8.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31289489A | 1989-02-17 | 1989-02-17 | |
| US312,894 | 1989-02-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2002142A1 true CA2002142A1 (en) | 1990-08-17 |
Family
ID=23213488
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2002142 Abandoned CA2002142A1 (en) | 1989-02-17 | 1989-11-02 | Process for increasing the useful life of a photovoltaic cell |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2002142A1 (en) |
-
1989
- 1989-11-02 CA CA 2002142 patent/CA2002142A1/en not_active Abandoned
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